﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;

namespace Asah.Web.Encryption
{
    /// <summary>
    /// Hash functions are fundamental to modern cryptography. These functions map binary 
    /// strings of an arbitrary length to small binary strings of a fixed length, known as 
    /// hash values. A cryptographic hash function has the property that it is computationally
    /// infeasible to find two distinct inputs that hash to the same value. Hash functions 
    /// are commonly used with digital signatures and for data integrity.
    /// </summary>
    public class Hash
    {

        /// <summary>
        /// Type of hash; some are security oriented, others are fast and simple
        /// </summary>
        public enum Provider
        {
            /// <summary>
            /// Cyclic Redundancy Check provider, 32-bit
            /// </summary>
            CRC32,
            /// <summary>
            /// Secure Hashing Algorithm provider, SHA-1 variant, 160-bit
            /// </summary>
            SHA1,
            /// <summary>
            /// Secure Hashing Algorithm provider, SHA-2 variant, 256-bit
            /// </summary>
            SHA256,
            /// <summary>
            /// Secure Hashing Algorithm provider, SHA-2 variant, 384-bit
            /// </summary>
            SHA384,
            /// <summary>
            /// Secure Hashing Algorithm provider, SHA-2 variant, 512-bit
            /// </summary>
            SHA512,
            /// <summary>
            /// Message Digest algorithm 5, 128-bit
            /// </summary>
            MD5
        }

        private HashAlgorithm _Hash;
        private Data _HashValue = new Data();

        private Hash()
        {
        }

        /// <summary>
        /// Instantiate a new hash of the specified type
        /// </summary>
        public Hash(Provider p)
        {
            switch (p)
            {
                case Provider.CRC32:
                    _Hash = new CRC32();
                    break;
                case Provider.MD5:
                    _Hash = new MD5CryptoServiceProvider();
                    break;
                case Provider.SHA1:
                    _Hash = new SHA1Managed();
                    break;
                case Provider.SHA256:
                    _Hash = new SHA256Managed();
                    break;
                case Provider.SHA384:
                    _Hash = new SHA384Managed();
                    break;
                case Provider.SHA512:
                    _Hash = new SHA512Managed();
                    break;
            }
        }

        /// <summary>
        /// Returns the previously calculated hash
        /// </summary>
        public Data Value
        {
            get { return _HashValue; }
        }

        /// <summary>
        /// Calculates hash on a stream of arbitrary length
        /// </summary>
        public Data Calculate(ref System.IO.Stream s)
        {
            _HashValue.Bytes = _Hash.ComputeHash(s);
            return _HashValue;
        }

        /// <summary>
        /// Calculates hash for fixed length <see cref="Data"/>
        /// </summary>
        public Data Calculate(Data d)
        {
            return CalculatePrivate(d.Bytes);
        }

        /// <summary>
        /// Calculates hash for a string with a prefixed salt value. 
        /// A "salt" is random data prefixed to every hashed value to prevent 
        /// common dictionary attacks.
        /// </summary>
        public Data Calculate(Data d, Data salt)
        {
            byte[] nb = new byte[d.Bytes.Length + salt.Bytes.Length];
            salt.Bytes.CopyTo(nb, 0);
            d.Bytes.CopyTo(nb, salt.Bytes.Length);
            return CalculatePrivate(nb);
        }

        /// <summary>
        /// Calculates hash for an array of bytes
        /// </summary>
        private Data CalculatePrivate(byte[] b)
        {
            _HashValue.Bytes = _Hash.ComputeHash(b);
            return _HashValue;
        }

        #region CRC32 HashAlgorithm
        private class CRC32 : HashAlgorithm
        {

            private uint result = 0xffffffff;

            protected override void HashCore(byte[] array, int ibStart, int cbSize)
            {
                uint lookup = 0;
                for (int i = ibStart; i <= cbSize - 1; i++)
                {
                    lookup = (result & 0xff) ^ array[i];
                    result = ((result & 0xffffff00) / 0x100) & 0xffffff;
                    result = result ^ crcLookup[lookup];
                }
            }

            protected override byte[] HashFinal()
            {
                byte[] b = BitConverter.GetBytes(result ^ 1);
                Array.Reverse(b);
                return b;
            }

            public override void Initialize()
            {
                result = 0xffffffff;
            }

            private uint[] crcLookup = { 0x0, 0x77073096, 0xee0e612c, 0x990951ba, 0x76dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, 0xedb8832, 0x79dcb8a4, 
            0xe0d5e91e, 0x97d2d988, 0x9b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 
            0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 
            0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 
            0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a, 
            0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 
            0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x1db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x6b6b51f, 
            0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0xf00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x86d3d2d, 0x91646c97, 0xe6635c01, 
            0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 
            0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 
            0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 
            0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, 
            0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 
            0x3b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x4db2615, 0x73dc1683, 0xe3630b12, 0x94643b84, 0xd6d6a3e, 0x7a6a5aa8, 
            0xe40ecf0b, 0x9309ff9d, 0xa00ae27, 0x7d079eb1, 0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 
            0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 
            0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c, 
            0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 
            0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 
            0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x26d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x5005713, 
            0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0xcb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0xbdbdf21, 0x86d3d2d4, 0xf1d4e242, 
            0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 
            0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 
            0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, 
            0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 
            0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d };

            public override byte[] Hash
            {
                get
                {
                    byte[] b = BitConverter.GetBytes(result ^ 1);
                    Array.Reverse(b);
                    return b;
                }
            }
        }

        #endregion

    }
}
